Moving Averages for the Ruby Array Class

moving_average.rb

# Examples
# [1,1,2,1,1,2,2].moving_average(2) => [1, 1, 1, 2]

class Array
  # Calculates the moving average 
  # given a Integer as a increment period
  def moving_average(increment = 1)
    return self.average if increment == 1
    a = self.dup
    result = []
    while(!a.empty?)
      data = a.slice!(0,increment)
      result << data.average
    end
    result
  end
  
  # Calculates the average
  def average
    (self.sum/self.size)
  end
end

You need to add Array#sum as well:

class Array
  def sum
    inject(0){|sum,x| sum + x }
  end
end